1. Kayak -- Flight search

More than a few trips begin with Kayak, one of the web's most popular travel services. Its mobile apps are great as well, allowing you to search flight details with ease on a mobile device.

I especially like the "explore" function, which presents you with a map of the world and the prices that it would cost to travel to various locations. For those who dream about traveling as much as they actually travel, the Kayak app is for you.

3. Lonely Planet Travel Guides

As you might expect, Lonely Planet has a lot of guides and phrasebook apps available in Apple's App Store. And just as you likely have more than one Lonely Planet book on your bookshelf, it's very possible that you're going to buy more than one Lonely Planet guide.

In order to manage your Lonely Planet purchases, you can add a sort of Lonely Planet catch-all app, which lets you access its entire catalog, including stored titles you've bought already.

4. TripIt -- Travel planner

All those confirmation mails that you get from hotels and airlines, you can simply forward along to plans@tripit.com, which will then magically generate a digital itinerary that you can refer to on your mobile device.

You can add multiple trips to TripIt if you're a frequent traveler, or just use it for a single vacation. TripIt was awarded Best Travel Mobile App for 2011 at the Webby Awards. It's not hard to see why.

5. Evernote -- Organizer

This popular digital note-taking app makes for a very helpful travel companion as well. I've not used it on trips myself, but Brett Terpstra recently pointed out that the app can really shine when you're on the road.

Take pictures of receipts and other important paperwork, and let Evernote's OCR help with the cataloguing. While I'm not a big fan of the Evernote desktop app (Brett's Notational Velocity wins out there), I think Evernote definitely wins when note-taking on the go.

6. UNESCO World Heritage -- Location guide

For travelers who would like a bucket list of amazing places to visit in their lifetime, the World Heritage app will do the trick.

It costs US$4.99, but that's a pretty good deal for a complete list of over 900 sites with 650 photographs as well. You can browse sites according to country or by classification, and favorite the ones you'd like to revisit later.

7. XE currency exchange

If you plan to hit multiple countries during your travels, it's always useful to have a currency conversion app handy. XE.com is one of the best known and most reliable currency-related sites on the net, and as you might expect, its app is no exception.

Just set your default currency and you can keep tabs on a number of others. Perhaps the best thing about it is that it remembers the most recently updated rate, so you can still convert with reasonable accuracy even when you don't have a connection.

8. Google Translate

Few companies bust language barriers better than Google, and the Google Translate app does this exceptionally well. Like the Google Translate web service, you can translate pieces of text with ease.

Of course the accuracy is not always perfect, but it's about as good as it gets. But where the app excels is in voice recognition. It allows you to speak in English (or another language) and it will translate what you said into the language of your choice.

If you've ever had difficulty making yourself understood to a speaker of a foreign language, then this free app will certainly help. Check out a video demo here.

9. Trip Journal -- Trip documenter

Currently on sale for US$0.99, Trip Journal is an award-winning travel app that lets you digitally document your trip on your iOS, Android, Bada or Symbian device.

With Google Maps/Earth integration, you get to map places that you've visited, geo-tag your photos and videos, or write blog entries too. Once you're finished you can export trips to Facebook where your friends can follow along on your path.

10. Airbnb -- Accommodation

Airbnb is an essential app for the tech-savvy backpacker, listing affordable accommodation around the globe -- ranging "from a private apartment to a private island."

In addition to searching for places to stay, you can also offer your own room for rent, if you'd like to make a little extra money. So far there are 150,000 places listed in 190 countries. In-app messaging to guests/hosts make communication frictionless, keeping all activity on your mobile.

12. Dropphox -- Photo sharing/storage

Dropphox is an application that sends your iPhone photos to the above-mentioned Dropbox, giving you a cloud backup only seconds after you snap off the picture.

If you share a Dropbox folder with friends or family, then they'll be notified of any photos you take in real time. The new version 1.1 supports geo-tagging of photos, although you'll need an Internet connection for this function to work.

Foreign correspondents would do well to install this one. It costs US$1.99.

13. Wikitude -- Location guide

This is a very handy application that draws a plethora of useful info about your surroundings from Wikitravel (a Wiki for travelers).

The display uses Augmented Reality to display annotations of nearby points of interest over the top of the regular camera display. Wikitude certainly looks useful, though it did throw an occasional 'cam view memory warning' for me.

14. Skype Wi-Fi-- Communication

An obvious addition to any travel app list would be Skype. But a less obvious addition to your app repertoire is Skype's recently released Skype Wi-Fi application.

If you've ever been in an airport browsing all the paid Wi-Fi hotspots, but not willing to pay for any, then this app might be of use. Skype Wi-Fi lets you pay using Skype Access, and on a per-minute basis too, so you only pay for as much time as you need, rather than a full hour or a day.

16. mTrip -- Location guide/planner

mTrip travel guides are available for most of the world's major cities including many in Asia, such as Tokyo, Shanghai, Singapore, Bangkok, and Hong Kong. There are offline maps for when you don't have an Internet connection, as well as a fancy AR feature that lets you browse points of interest nearby.

There's a function that lets you send virtual postcards to friends and family, either via email or on Facebook. The trip auto-generated itineraries are slick, mapping out the places you plan to go in a given day according to the types of places you enjoy (i.e. museums, parks, etc).

17. Highlights for iPad -- Hot spot finder

As someone who isn't a huge fan of Foursquare or Gowalla, I was pretty tickled to stumble upon highlights. This clever app takes all the most popular places that people check into on those platforms, and makes them browsable via a convenient map.

So if you find yourself in a strange location and you want to find the most popular places in the area, just fire up Highlights to see where people check in the most. You can scan reviews and photos, and add locations to your personal planner. The app isn't free, but at US$0.99 it's pretty close.

18. TripAdvisor -- Travel reviews

TripAdvisor is another wildly popular travel application that features a number of practical uses from finding flights to hunting hotels.

Perhaps the biggest plus is the ability to browse so many reviews from places of interest. Like many of the travel applications we've featured on this list, TripAdvisor also comes with an augmented reality function called "Live View."

19. Google Goggles -- Image search/translate

This innovative app has received much attention since it first hit the Android Market. It lets you search on Google by just taking a picture. So, if you're visiting a landmark, you can take a picture which Google will then analyze and provide results for.

More practical however is the OCR function, which will let you take pictures of foreign text, which you can then run through Google Translate. Google has a demo video here if you'd like to learn more.

20. Orient -- Location finder

This is a very simple app, but it's one of my favorites. Orient gives you a sort of compass view of a list of locations, showing you where certain locations are in relation to you. When you fire up the app, it shows major world cities.

But to get the full benefit, try adding all the places you plan to visit during your next day trip. If you're doing a walking tour of a city, Orient show you the direction and distance of all your destinations.

Orient Lite is a free application, but there is a US$0.99 version with slick AR functionality.

21. AroundMe -- Location finder

This aptly named app tells you all the points of interest that are located near you. It detects your current location, and lets you select from categories like bars, cafés, hospitals, and hotels to filter though the results.

You can review the places on a map, or try the AR feature with markers overlaid on your phone' camera viewfinder. It's undoubtedly a quality app, but its mileage may vary as some locations do not have as many results as others (I tried Tokyo, and the results were not so helpful).

22. Hotels.com -- Accommodation

You've probably already figured out what this app does. The Hotels.com app lets you search and book hotels all from your mobile phone. The location-aware function makes it possible to find the closest hotel where you are currently.

Users can also access their reservation information even without an Internet connection. Even if you aren't a member of Hotels.com, the app is still extremely useful if you're in a new city looking for a place to stay.

23. Converse -- Translate

This iPad application is a very innovative one, but it isn't without flaws. Much like the Google Translate app, Converse aims to solve travelers' language woes with a real-time mobile solution.

With keyboards on opposite sides of your iPad, two people can face each other and communicate by typing on the iPad. So far, messages can be translated into English, French, Spanish, German, Portuguese, Italian, and Dutch.

But the biggest issue is that it requires an internet connection to work, so travelers on the road might be left to their pocket phrasebooks more often than not. However for someone like a hotel concierge with constant access to a connection, it could be a very snazzy work tool.

25. Skyscanner -- Flight search

If you need to check flight availability and prices on the go, Skyscanner is a must for your iOS or Android device. It's a free application that covers over 670,00 flights on more than 600 airlines.

The scroll date selection is pretty convenient, and I got a kick out of the airplane loading bar that appeared while I was waiting for search results. For anyone who flies regularly, this is a great app.

27. Nursery Rhymes with StoryTime -- Remote storytelling

While most of the apps on this list focus on helping you have fun, we can't forget about the people we've left at home. That's the spirit behind this Nursery Rhymes application, which lets travelers read stories to loved ones from a remote location.

Available for both iPhone and iPad, Nursery Rhymes features wonderful artwork that both parents and kids can enjoy. It's available in the app store for US$3.99. Check out the promo video here.

28. uPackingList -- Travel organizer

It's debatable whether or not you really need an app to help you put your stuff in a suitcase. But for those who do, uPacking List provides an assortment of common items that you can choose from and add to your list.

In the interests of testing the app, I made up a hypothetical list as a demonstration (pictured). The app is ad-supported, but there's a paid option if you don't like the advertising.

30. Knapsack -- Travel organizer

While this list is practically all mobile apps, I'm going to include one exception to the rule. Because after all, more than a few of us bring along a laptop when we travel, so it stands to reason that a Mac travel app could be a useful addition.

Knapsack for Mac is a useful multi-purpose travel app that includes map integration, itinerary and iCal functions, as well as to-do lists. It costs US$29, but give the free demo a try first to see if it's a good fit for you.

31. World Atlas HD -- Maps

For travelers with stops in multiple countries, this app by the National Geographic Society is a good reference. The design of the maps included with this app are a refreshing change from normal digital maps.

But if you have an Internet connection, you can still zoom in to view small details on Microsoft Bing maps. You can also browse interesting data and statistics regarding the countries you plan to visit.

32. Expensify -- Finance organizer

This popular app is a great companion for business travelers. Use Expensify to keep track of your purchases and transactions by syncing with your credit cards and bank accounts.

The app also acts as a receipt scanner, taking advantage of your mobile phone's camera. After your trip, you're sent a PDF report of all your spending which you can submit to your company for reimbursement.

33. GateGuru -- Airport guide

If you're a person who spends a lot of time in airports, GateGuru will be a godsend. This app contains a detailed list of places within 120 airports worldwide, including different terminals, cafés, restaurants and gift shops.

There are lots of reviews available for some airports, although when I browsed Narita it was sorely lacking. Nonetheless, having access to so many airport maps on the go is very helpful, especially if you find yourself running late and unsure of where you need to go.

34. FlightTrack Pro -- Flight information

This award-winning app is one of the most expensive on our list at US$9.99, but it's also one of the most practical. FlightTrack Pro integrates with TripIt, importing your flight itinerary so you can track its status in real time.

Flight maps show your progress as well as the current weather. Knowing the status of your flight allows you to share it with people who may be waiting on the ground, via email, Facebook, or Twitter.

One app review claimed that on occasion the app provides even better information than the airline!

35. Tripline -- Travel documenter

Although still in beta, Tripline is a really fun app to play with while traveling. You can create a mapped timeline of your travels by checking into a location, taking a photo or video, or jotting down a few notes about your stop.

When you return home, you can replay the entire trip in an interactive presentation, reviewing your notes and collected media that documented your time on the road.

36. My TSA -- U.S. travel information

For travelers passing through the United States, it certainly helps to be familiar with the rules and regulations of the TSA. The My TSA app tells you exactly that, with a practical travelers guide telling you what sorts of things you can and cannot take with you when you fly.

The app also provides flight delay information for airports nationwide, as well as tips for how to prepare for security checkpoints.

37. Wi-Fi Finder

Many of the apps on this list are dependent on an Internet connection. This application helps ensure that you have one by helping you find one of over 500,000 locations listed worldwide.

You can filter according to whether a hot spot is free or paid, although in some countries, the results are less than ideal. I explored some of the regions for Asia, and many places didn't show a lot of results.

40. Fotopedia Heritage -- Image-based location guide

Another great way to browse UNESCO World Heritage sites is by using the award-winning Fotopedia Heritage app. You can browse all world heritage sites on a single map, and click through to view information about them as well as stunning photography.

It's available for both iPhone and iPad, although if you want to experience the full benefit of the application, try it on the iPad.

41. aMetro -- Transport information

Most of the major world cities will have applications for navigating city trains or subways. For bigger cities like Tokyo, there are more robust options available.

But if you'd like a single app that gives you access to transit systems all over the world (in 180 cities to be exact) then aMetro is the way to go. There's a video demo of the app in action available on YouTube if you'd like a preview.

42. Convert Clothes -- Clothing size converter

While shopping abroad, travelers often run into the dilemma of figuring out foreign sizes. Thankfully the Convert Clothes app for iPhone has you covered.

Whether you're shopping for shoes, pants, a shirt, or even a bra, the app converts sizes for a number of different countries (Britain, Japan, Korea, France, for to name a few). It's a simple app that performs a simple task, and best of all it's free.

43. iMovie -- Video

I nearly overlooked this one, but if you decide to shoot any video on your trip using an Apple mobile device, then you're probably going to want to drop US$5 on iMovie.

Choose a theme and edit your video and add music or sound effects, and share with your friends online when you're finished (publish to YouTube, Facebook, or Vimeo). Once you get the hang of video editing on a mobile device, you'll have one less reason to bring along your laptop.

44. Tipping Bird -- Tipping information

Tipping is a practice that can vary from one country to the next. Indeed in many cultures, they might not even tip at all.

The Tipping Bird app lets you select a country, and then it tells you a recommended tip for typical situations, such as in restaurants or taxis. You can also convert the currency to your own, just so you have a relative idea of how big a hole you're burning in your pocket.

45. EveryTrail -- Location guide

For those who especially enjoy the great outdoors, EveryTrail is an important app to bring along. In addition to letting you map your route via GPS, EveryTrail also contains the shared trails of other users.

So if you find yourself in a strange land in need of a recommended route, try firing up EveryTrail to see if there are any shared guides for your area.

46. Postagram -- Communication

While sharing postcards online is great for most people, it's possible that you might have a few loved ones who have yet to join the digital world.

Postagram solves this problem by letting you create a postcard with photos on your iPhone, and then ships it as a physical postcard to whoever you choose. There is a charge of course, but there always is when sending mail, right?

48. Trip Splitter -- Finance organizer

This app is a handy way to divy up travel costs if you're on a trip with friends. Most of the time, whoever has the cash readily available will pay, but quite often it can be tricky to remember who paid for what at the end of your travels.

Trip Splitter (for iPhone or iPad) helps you do this, although the less-than-intuitive interface does take some getting used to. There's a free version that supports inputs for two travelers, but if you have more people whose payments you want to track, you'll want the paid version (US$1.99).

Rick Martin lives in Tokyo where he writes about technology in Japan, China, and around Asia. He contributes to TechInAsia.com, The Japan Times and a few other publications. He can be reached via his website, 1Rick.com.